Field with good jumper, furlong to go (3)
I believe the answer is:
lea
'field' is the definition.
(lea can mean a meadow or field of grass)
'jumper furlong to go' is the wordplay.
'jumper' becomes 'flea' (something that jumps).
'furlong' becomes 'f' (abbreviation for furlong, a unit of length).
'to go' is a deletion indicator.
'flea' with 'f' taken away is 'LEA'.
'with good' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for lea that I've seen before include "grazing area" , "Poetically, a piece of meadow or pasture" , "''The lowing herd winds slowly o'er the ... '' (Gray)" , "Field" , "Grazing land" .)